1. Field of the Invention
The present invention relates to a method for manufacturing a microintegrated structure with buried connections, in particular an integrated microactuator for a hard disk drive unit.
2. Description of the Related Art
As known, hard disks are the most widely used medium for storing data in personal computers; consequently, they are produced in very large quantities and the maximum data storage capacity increases year by year. Hard disks are read and written by a drive unit, the general structure whereof is shown in FIGS. 1 and 2 and is described hereinbelow.
In particular, FIG. 1 shows a drive unit 1 of rotary type comprising a motor 2 (also called xe2x80x9cvoice coil motorxe2x80x9d) fixed to a support body 3 usually called E-block owing to its E-shape when viewed laterally (see FIG. 2). The support body 3 has a plurality of arms 4, each carrying a suspension 5 formed by a steel blade fixed in cantilever fashion. Each suspension 5 has, at its end not fixed to the support body 3, a joining piece, called gimbal or flexure 8, also made of steel and carrying a read/write transducer also called slider 6 and arranged (in the operative condition) facing a surface of a hard disk 7.
The slider 6 is formed by a support body bearing, fixed thereto, a magneto/resistive and inductive R/W head 9 forming the actual read/write device; electric wires (not shown) extend from the R/W head 9 along the flexure 8 and the suspension 5 as far as a signal processing device (also not shown) fixed to the mother board of the personal computer or other apparatus comprising data storage hard disks.
In the read/write devices for hard disks currently commercially available, the slider 6 is glued directly to the flexure 8. To obtain a more precise and fine control of the position of the slider 6, it has already been proposed to use a double actuation stage, with a first courser actuation stage, comprising the motor 2 displacing the assembly formed by support body 3, suspension 5, flexure 8 and slider 6 across the hard disk 7 when carrying out an approximate track search, and a second actuation stage, comprising an integrated microactuator 10 arranged between the slider 6 and the flexure 8 and performing finer control of the position of the slider 6 when searching for a track.
Different technologies have been proposed for manufacturing the integrated microactuator, such as surface micromachining, which use polycrystalline surface layers of semiconductor material deposited over a semiconductor material wafer, electrogalvanic growth, or ad hoc processes other than those normally used in microelectronics.
The proposed methods using the technique of surface micromachining have the drawback that they do not allow integration of the microactuator with the control and drive circuits or involve low-output and very costly post-machining steps.
Other known solutions involve the use of ductile materials such as nickel or its alloys. However, these solutions are also not free from drawbacks. Although nickel can dissipate internally the mechanical energy, its plastic behavior makes final quality control of the end device particularly expensive and difficult.
European patent application No. 97830537.3, dated Oct. 29, 1997 and owned by STMicroelectronics, S.r.l., describes a method for manufacturing an integrated microactuator formed in the epitaxial layer of a semiconductor material wafer. In particular, according to the solution described in this patent application, buried interconnection regions are formed in a monocrystalline silicon substrate, and then a sacrificial region and isolating regions, comprising silicon oxide, are formed on the substrate surface; a polycrystalline silicon seed layer is then deposited on the substrate and the silicon oxide regions and then an epitaxial layer is grown, which is polycrystalline above the silicon oxide regions and elsewhere monocrystalline; the electronic components of the circuitry are then formed within and above the monocrystalline portion of the epitaxial layer, while the conductive regions necessary for forming the microactuator are formed in the polycrystalline portion; then the epitaxial layer is etched to define and separate from one another a rotor and a stator; finally, the sacrificial region is removed to free the movable structures from the rest of the wafer.
This solution, although very advantageous as regards the mechanical characteristics, owing to the reduced risk of sticking of the movable structures and the lower manufacturing costs compared to other known solutions, has the problem that PN junctions are present between the buried N-type connection regions, necessary for biasing the various regions of the actuator, and the P-type seed layer necessary for epitaxial growth in the mutually facing zones. These PN junctions have low and in particular non-controllable breakdown voltages that limit the applicable operative biasing voltages of the microactuator.
An embodiment of the invention overcomes the drawback associated with the preceding solution, increasing the usable biasing voltage values.
An embodiment is directed to a method for manufacturing a microintegrated structure, typically a microactuator for a hard-disk drive unit and includes the steps of: forming interconnection regions in a substrate of semiconductor material; forming a monocrystalline epitaxial region; forming lower sinker regions in the monocrystalline epitaxial region and in direct contact with the interconnection regions; forming insulating material regions on a structure portion of the monocrystalline epitaxial region; growing a pseudo-epitaxial region formed by a polycrystalline portion above the structure portion of the monocrystalline epitaxial region and elsewhere a monocrystalline portion; and forming upper sinker regions in the polycrystalline portion of the pseudo-epitaxial region and in direct contact with the lower sinker regions. In this way no PN junctions are present inside the polycrystalline portion of the pseudo-epitaxial region and the structure has a high breakdown voltage.